Cut 1/4 pound of the tuna against the grain into 12 thin slices. Finely chop the other 1/2 pound for the tartare.
To prepare the tartare base, combine all the ingredients and mix well. Add the chopped fish and stir lightly to combine.
To prepare the crispy wontons, in a saucepan, pour in the oil to a depth of 1-inch and heat to 375 degrees. Add the wonton skins and fry, turning once, for 8 to10 seconds on each side, until light golden brown. Keep the wontons flat by using tongs to uncurl them. Using a wire skimmer, transfer to paper towels to drain. Allow to cool.
In a bowl, combine all the ingredients for the dressing and mix well.
To assemble, first roll the tuna slices up into rose-shaped bundles. Reserving 2 tablespoons of the radish sprouts, stack in the following order: wonton skin, 1/6 of the tartare mixture, shiso leaf, wonton skin, 1/6 of the smoked salmon, radish sprouts, wonton skin, 2 tuna rolls.
Sprinkle the top of the each napoleon with the reserved radish sprouts. Drizzle 3 tablespoons of the dressing around each plate. Garnish with pickled ginger and tobiko.
To serve, cut through the entire stack with a knife, and smash the layers together with a fork to blend the flavors.